1. Field of the Invention
This invention is in the field of air filters and, more specifically, in the field of air filters used for medical and therapeutic purposes.
2. Description of the Prior Art
Current inhalation therapy procedures often require filtration of the air administered to a patient. The filters used must be autoclavable for sterilization and/or disposable for avoiding patient-to-patient contamination. Users also want the pressure-drop across a filter be small (even at high capacity) while the total physical size of the filter remains small.
When a filter designer attempts to meet all these criteria, he may find that they actually work against each other. For example, to squeeze a lot of filter surface into a compact container, the filter designer may choose an accordian shaped pleated filter media, but then sealing the unusual zigzag shaped edges of the pleated filter media at a low cost is a problem. One solution to the problem of sealing a pleated filter media in a container was found by Rose et al., U.S. Pat. No. 3,494,466, where foils of thermoplastic material were heatsealed to the edge of the material and then a ring of adhesive material was used to seal the foil wrapped filter to the container wall. Another type of filter invented by Gronholz, U.S. Pat. No. 3,712,033, seals the end pleats of a pleated filter media by means of a clamp formed from a slot, an upstanding member, and a rigid screen end. Then, a hot melt adhesive is used to seal the filter's zigzag sides to end caps. Daigle et al. developed an improvement of the Gronholz's filter, U.S. Pat. No. 3,778,985, which uses a specially formed flexible panel end in place of Gronholz's rigid screen for clamping. Clamping the end pleats of a pleated filter media is also a characteristic of a patent to Rosenberg, U.S. Pat. No. 3,815,754; once the end pleats are clamped in place, they are permanently sealed by a weld or bond and then an end cap is welded or bonded to each zigzag edge of the filter.
These filters represented a limited advance over the prior art filters of their day, but the rising cost of materials and labor for medical products has created an urgent need for an air filter of even simpler construction requiring fewer manual steps for its assembly without sacrificing quality or filter efficiency.